Olefin polymerization catalysts comprising a metallocene and an aluminum alkyl component were first proposed in about 1956. Australian patent 220436 proposed for use as a polymerization catalyst a bis-(cyclopentadienyl) titanium, zirconium, or vanadium salt as reacted with a variety of halogenated or unhalogenated aluminum alkyl compounds. Although such complexes were capable of catalyzing the polymerization of ethylene, such catalytic complexes, especially those made by reaction with an aluminum trialkyl, had an insufficient level of catalytic activity to be employed commercially for production of polyethylene or copolymers of ethylene.
Later it was found that certain metallocenes such as bis-(cyclopentadienyl) titanium, or zirconium dialkyls in combination with aluminum alkyl/water cocatalyst form catalyst systems for the polymerization of ethylene. Such catalysts are discussed in German Patent Application 2,608,863 which discloses a polymerization catalyst for ethylene consisting of bis-(cyclopentadienyl) titanium dialkyl, aluminum trialkyl and water. German Patent Application 2,608,933 discloses an ethylene polymerization catalyst consisting of a cyclopentadienyl zirconium salt, an aluminum trialkyl cocatalyst and water. European Patent Application No. 0035242 discloses a process for preparing ethylene and atactic propylene polymers in the presence of a halogen free cyclopentadienyl transition metal salt and an alumoxane. Such catalysts have sufficient activity to be commercially useful and enable the control of polyolefin molecular weight by means other than hydrogen addition--such as by controlling the reaction temperature or by controlling the amount of cocatalyst alumoxane as such or as produced by the reaction of water with an aluminum alkyl.
To realize the benefits of such catalyst systems, one must use or produce the required alumoxane cocatalyst component. An alumoxane is produced by the reaction of an aluminum alkyl with water. The reaction of an aluminum alkyl with water is very rapid and highly exothermic. Because of the extreme violence of the reaction, the alumoxane cocatalyst component has, heretofore, been separately prepared by one of two general methods. Alumoxanes may be prepared by adding an extremely finely divided water, such as in the form of a humid solvent, to a solution of aluminum alkyl in benzene or other aliphatic hydrocarbons. The production of an alumoxane by such procedures requires use of explosion-proof equipment and very close control of the reaction conditions in order to reduce potential fire and explosion hazards. For this reason, it has been preferred to produce alumoxane by reacting an aluminum alkyl with a hydrated salt, such as hydrated copper sulfate. In such procedure a slurry of finely divided copper sulfate pentahydrate and toluene is formed and mantled under an inert gas. Aluminum alkyl is then slowly added to the slurry with stirring and the reaction mixture is maintained at room temperature for 24 to 48 hours during which a slow hydrolysis occurs by which alumoxane is produced. Although the production of alumoxane by a hydrated salt method significantly reduces the explosion and fire hazard inherent in the wet solvent production method, production of an alumoxane by reaction with a hydrated salt must be carried out as a process separate from that of producing the metallocene alumoxane catalyst itself. This process is also slow and produces hazardous wastes that create disposal problems. Further, before the alumoxane can be used for the production of the active catalyst complex, the hydrated salt reagent must be separated from the alumoxane to prevent it from becoming entrained in the catalyst complex and thus contaminating any polymer produced therewith.
Only in those situations wherein a hydrated material is of a chemical composition acceptable as a filler material for a filled polyolefin composition may it be used to produce a metallocene/alumoxane catalyst complex by direct reaction with an aluminum alkyl solution. Hence U.S. Pat. No. 4,431,788 discloses a process for producing a starch filled polyolefin composition wherein an aluminum trialkyl is first reacted with starch particles of a moisture content below 7 weight percent. The starch particles are then treated with a (cyclopentadienyl)chromium, titanium, vanadium or zirconium alkyl to form a metallocene alumoxane catalyst complex on the surface of the starch particles. An olefin is then polymerized about the starch particles by solution or suspension polymerization procedures to form a free-flowing composition of polyolefin-coated starch particles. German Patent 3,240,382 likewise discloses a method for producing a filled polyolefin composition which utilizes the water content of an inorganic filler material to directly react with an aluminum trialkyl and produce thereon an active metallocene alumoxane catalyst complex. Polymer is produced by solution or gas phase procedures at the filler surface to uniformly coat the filler particles and provide a filled polymer composition.
German Patent 3,240,382 notes that the activity of a metallocene alumoxane catalyst is greatly impaired or lost when prepared as a surface coating on an inorganic material. Although German Patent 3,240,382 suggests that an inorganic material containing absorbed or adsorbed water may be used as a filler material from which the alumoxane cocatalyst component may be prepared by direct reaction with an aluminum trialkyl, the only water containing inorganic filler materials which are identified as capable of producing the alumoxane without adversely affecting the activity of the metallocene alumoxane catalyst complex are certain inorganic materials containing water of crystallization or bound water, such as gypsum or mica. German Patent 3,240,382 does not illustrate the production of a catalyst coated inorganic filler material wherein the inorganic material is one having absorbed or adsorbed water. Nor does German Patent 3,240,382 describe an inorganic filler material having absorbed or adsorbed water which has surface area or pore volume properties suitable for service as a catalyst support for a liquid or slurry phase polymerization procedure.
European Patent 0,170,059 discloses a process for forming alumoxanes for catalysts in polymerization of olefins. Specifically, it discloses adding a finely divided porous solid, e.g., silica dioxide or aluminum oxide, to a non-aqueous medium, adding water to that medium and then mixing in aluminum trialkyl to form alumoxane. After the alumoxane is formed, a transition metal compound (metallocene) is added, followed by the monomer. Since water and porous solid are added separately into the reactor, this technique basically involves adding aluminum trialkyl to water which yields a catalyst not being attached to any solid support. The catalyst produced in this process can cause severe reactor fouling during the polymerization due to the nature of the unsupported catalyst.
It would be desirable to devise an economical, reproducible, and clean process whereby an active supported metallocene/alumoxane catalyst could be produced for use in liquid or slurry phase polymerization. To be economical the process should dispense with the requirement of producing the alumoxane component as a separate component apart from the procedure by which the catalyst itself is prepared. To be reproducible, the procedure should specify the exact procedure of producing the porous solid material which contains the right amount of water absorbed or adsorbed on its surface so that it could generate alumoxane with a high degree of catalytic activity. To be clean, the catalyst produced in the polymerization system should not cause the fouling of the reactor during the polymerization so that it could be applied to commercial production.